/*
 * Copyright (c) 2011-2012 Alexander Dubu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * o  Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * o  Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * o  Neither the name Axil nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

package axil.stdlib.core.construct;

import axil.api.AxilObject;
import axil.api.extend.Environment;
import axil.api.extend.Parameters;
import axil.api.extend.Source;
import axil.compiler.api.Emitter;
import axil.compiler.ast.FunctionCallNode;
import axil.compiler.ast.Node;
import axil.vm.opcode.Opcode;

import java.util.List;

import static axil.framework.Functions.nv;
import static axil.framework.Functions.replace;


/**
 * The Axil switch mechanism, which is a multi-branch conditional construct:
 *
 * 		switch(expr,
 * 			when(value, body),
 * 			when(value, body),
 * 			[...]
 * 			of(expression, body),
 * 			else(body)
 * 		)
 */
public class Switch extends Special implements Emitter {
	private AxilObject value;
	private Conditional[] cases;


	/**
	 * This constructor is used only when creating anonymous instances suitable
	 * for loading the function definition. Use this with caution! This is not
	 * meant to create an executable object.
	 */
	public Switch() {
	}


	private Switch(Source source, AxilObject value, Conditional[] cases) {
		super(source);
		this.value = value;
		this.cases = cases;
	}


	/**
	 * Relink this instruction, replacing the bad variable ID with the good
	 * variable ID. This is used when linking code that contains forward
	 * references, allowing us to compile in a single pass, but correct later.
	 */
	public void relink(int bad, int good) {
		replace(value, bad, good);
		for (Conditional cond : cases) {
			cond.relink(bad, good);
		}
	}


	/**
	 * Emit a new instance of this function using the indicated arguments. This
	 * method can safely assume that the number of arguments required are being
	 * provided.
	 */
	public Opcode emit(Source source, List<Node> args) {
		final int size = args.size();
		Conditional[] list = new Conditional[size - 1];
		for (int i = 1; i < size; i++) {
			Conditional cond;
			Node n = args.get(i);
			if (n instanceof FunctionCallNode) {
				FunctionCallNode fc = (FunctionCallNode)n;
				if (fc.function().equals("of")) {
					cond = new Of(n, fc.arg(0).emit(), fc.arg(1).emit());
				} else {
					if (fc.function().equals("when")) {
						cond = new When(n, fc.arg(0).emit(), fc.arg(1).emit());
					} else {
						if (i == (size - 1)) {
							if (fc.function().equals("else")) {
								cond = new Else(n, fc.arg(0).emit());
							} else {
								throw compile(n, "expecting-of-when",
								              nv("other", n.what()));
							}
						} else {
							throw compile(n, "expecting-of-when",
							              nv("other", n.what()));
						}
					}
				}
			} else {
				if (i == (size - 1)) {
					/*
					 * In this case, this is the last expression and it is not
					 * a conditional. So, we simply wrap it in an else() so that
					 * the values are a uniform type. Very much in keeping with
					 * the lisp cond() function.
					 */
					cond = new Else(n, n.emit());
				} else {
					throw compile(n, "expecting-of-when", nv("other",
					              n.what()));
				}
			}
			list[i - 1] = cond;
		}
		return new Switch(source, args.get(0).emit(), list);
	}


	/**
	 * Evaluate this object in the given context and environment. A non-null
	 * object must be returned.
	 */
	protected AxilObject evaluate(Environment env, Parameters params) {
		AxilObject v = value.eval(env, params);
		for (Conditional c : cases) {
			if (c.select(env, params, v)) {
				return c.eval(env, params);
			}
		}
		throw evaluation(params, "switch-fall-through");
	}
}
